1. Acute inflammatory monoarticular arthritis
- DDx: gout, pseudogout, septic joint, osteomyelitis, trauma (rarer: first episode of RA, reactive arthritis)
- Is an absolute indication for arthrocentesis, unless you're absolutely sure it's gout:
- Signs that point to gout:
>1 attack of acute arthritis (i.e. history of gout)
Maximal inflammation in <1 day ("thunderclap onset")
Monoarthritis
Joint erythema
1st MTP involvement ***
Unilateral MTP arthritis
Unilateral tarsal acute arthritis
Tophus
Asymmetric joint swelling
Hyperuricemia
Bone cysts without erosion on X-ray
Negative joint fluid culture
- 6 or more of the above criteria for diagnosing gout: Sens/Spec – 87%/96%, LR + 22, LR - 0.13
- 5 or more: Sens/Spec – 95%/89% LR + 8.6, LR - 0.005
2. Gout 
-Acute: colchicine (dose to the major side effect, which is diarrhea), prednisone PO or joint injection, NSAIDs
-Chronic: allopurinol, febuxistat (if they can't tolerate allopurinol bc of renal insufficiency), probenicid (if they are underexcreters)
-Also affects kidney (urate nephropathy ie CKD without any cause other than gout)
3. CPPD/Pseudogout
- Clinically resembles OA, treat it as if it was OA
- Pseudo RA
- Affects the knee
- Xray: linear calcifications within joint space.
- Due to hypercalcemia (occult hyperparathyroidism is most common cause)
- Treat with colchicine, NSAIDs, treat hyperparathyroid if they have it
4. Septic joint
- Either GC or Staph
- GC: triad of septic joint, tenosynovitis (87%), fever (50%), skin lesion (90%), positive blood cx (43%), because its a higher grade bacteremia than staph.
- Tenosynovitis: back of hands, tendons all inflamed, can't bend hands.
- Staph: less risk of all of the above sx. usually in people with a reason to get staph in their blood (IV drug use, recent surgery, port/dialysis cath, etc)
- Hand and such you can just give IV abx
- Big joints (hip) need to be washed out either in the OR or at bedside.
5. Lyme disease
- Nymph form of ixodes tick is the one that carries lyme disease (Nymphs are much tinier than adult ticks)
- Single dose 100 mg doxy prevents lyme. However the % of lyme-carrying, nymph, ixodes/deer ticks are so rare that it'd be egregious overtreating to prophylax everyone.
- Acute lyme tx: 21 days of doxy.
- If you don't treat lyme, the next things that you get are heart (heart block), brain (headache, meningitis), then 1-6 months out then you get joint pain (knee most common)
- Anything after acute phase you need IV ceftriaxone
- Can also get jarisch-herxheimer reaction as well with initiation of treatment... so warn your patients they may feel a lot worse before they feel better.
- Endemic areas: coastal mideast, northwest wisconsin, some in california
- Lyme rash hurts
6. RA
- Metatarsals, wrists
- In a younger person, lupus can cause similar symptoms
- Workup: ESR/CRP, RF, anti-CCP (specific), x-ray (erosive joint), rheumatoid nodules (over bony joints like knuckles and olecranon, LR +22)
- Tx: acutely, steroids and NSAIDs, once you get a diagnosis then 20mg/week of methotrexate and as much steroids as you need to control symptoms. After you fail that, then biologics (like remicade). Recent NEJM study showed that people who failed mtx randomized to remicade vs plaquenil, that many people did well on plaquenil.
- 20 mg one time a week. Then you wean by 2.5 mg every 2 months or so. Most people need at least ~12.5 mg.
7. Psoriatic arthritis
- Psoriasis, nail findings, DIP involvement, "sausage digits" - where whole finger is inflamed. Because you get enthasopathy (inflammation of tendon insertions) as well as arthritis.
- Even if people say they don't have psoriasis, look closely (umbilicus, genitals, etc) for hidden psoriasis.
- Arthritis mutilans, telescoping digits -- destruction of joint with tendon still pulling down, so fingers shorten.
8. Seronegative (ie ANA neg, RF neg) spondyloarthropathies (can affect spine) 
- Often cause asymmetric inflammation (one knee, one ankle), enthasopathy is common
- Chronic, polyarticular
- Psoriatic, Ankylosing spondylitis, reactive arthritis/reiter's, IBD
9. Lupus
- Hold on immune workup until you have 3+ clinical sx (i.e. malar/discoid rash, cardiac/pulmonary serositis, renal disease, arthritis) to avoid overdiagnosing and sending ANAs on everyone, b/c ANA is so nonspecific
10. Erythema nodosum
- Seronegative spondyloarthropathies (esp IBD), sarcoid
- Rheumatic fever (JONES criteria are major - migrating polyarthritis, peri/myo/endocarditis, subQ nodules, erythema nodosum, syndenham's chorea, minor criteria - fever, joint pain, PR prolongation, elevated ESR/CRP)